The invention involves a device for checking the compaction, in particular, of black top pavement in street and roadway construction, using a vibration roller drum that is provided with a compaction checking device.
It is well-known in the prior art that when processing the ground using compaction devices, a more economic execution of the construction work is possible through the use of constant compaction checks. Customarily, these compaction checking devices are based on the method of measuring the reflections of the vibrations which are transferred by the compaction device during vibrational compaction of the ground. Hardly any vibrational energy is reflected back by a very loose material, but on the other hand, ground that is already greatly compacted or in the extreme case, a massive concrete slab, returns almost the entire vibrational energy back to a vibration roller drum.
Compaction checking devices of this type can, for example, be impulse transducers attached to the roller frame, which act together using an acceleration measurement process with a statistical performance.
By an acceleration transmitter of this type on the roller frame, however, impact forces might also be registered which occur when the vibrating tires of a vibration roller drum work the surface to be compacted.
If for compaction checking devices of this type, the compaction no longer changes in spite of an increasing amount of compaction passages, the intended highest density has been achieved with this specific compaction device. This density has already been exceeded if the value determined decreases again, since a loosening of the ground is occurring.
Compaction checking devices of this type reach their limits, however, when they are applied to compacting black tops:
In determining the dynamic ground rigidity on asphalt layers with the known methods described above, the rigidity and thus the density of the asphalt layer can thus not be determined exactly, since the rigidity of the asphalt layer is a function of the temperature to a large extent. An exact temperature measurement of the asphalt layer is not possible. In particular, the surface temperature of the asphalt layer, which is easy to determine, can not be taken as a measure for the temperature of the entire layer, because, among other reasons, the temperature of the surface is too greatly dependent on environmental influences such as the prevailing wind or rain, which have, however, no effect on the temperature on the inside of the asphalt layer.
Finally, the values determined in the black top structure when it is traveled over by known compaction checking devices are not meaningful enough with regard to the dependence of the dynamic rigidity of the asphalt layer on the temperature that is prevalent in it.
In particular, this rules out the method that has been pursued until now in ground compaction, in which the values determined when first traveled over by a vibration roller drum that has a compaction checking device are stored, and then compared to the values determined when traveled over for a second time, in order to make conclusions about the compaction from the differences. The temperature changes in the asphalt layer occurring between the two passages with one machine have an effect that can not be compensated for.
The object of the invention presented here is thus to further develop a device for checking compaction so that it also produces measurement data and results for black top in street and roadway construction, which do not have the disadvantages mentioned above.
This object is achieved according to the invention in that the device for checking the compaction has a second vibration roller drum that is provided with a second compaction checking device and which is coupled to the first vibration roller drum essentially following it exactly in its track whereby an evaluation unit is present which compares the measurement results of the two compaction checking devices.
The invention has the advantage that by the second vibration roller drum being coupled to the first vibration roller drum, the passage of the second roller drum follows immediately after the first so that the time period between the two passages can be neglected with regard to a temperature change in the asphalt layer. Furthermore, by the evaluation unit that is present, which compares the measurement results of the two compaction checking devices arranged in the first or second vibration roller drums, effects can also be compensated for, when because of the measurement depths present, the rigidity of the underground lying below the asphalt layers is proportionately measured at the same time. This effect of the underground rigidity can be eliminated by the subtraction of differences in the measurement results during the comparison.
The invention is thus also based on the realization that the change of the asphalt rigidity is a quite good reference value for the increase in the compaction progress of the asphalt.
By the coupling of the two vibration roller drums according to the invention, which allows the second roller drum to essentially follow the first roller drum in the same track, an additional peculiarity is taken into account in black top construction, which represents a considerable difference from the customary ground compaction using vibration roller drums: Whereas in customary compaction operations, the individual compaction paths are next to each other track to track in parallel, in black top construction, in order to prevent the formation of grooves, a looped and meandering drive path is selected, which can normally not be reproduced in a separate second passage.
By the coupling of the two vibration roller drums in the same track, this problem is solved.
As most advantageous, this coupling in the same track can be achieved in a tandem roller. However, it is also within the context of the invention to provide the vibration roller drums in two separate single drum rollers, which can then be coupled together especially via a computer-supported tracking process. In this computer-supported tracking process, for example, a satellite-supported Global Positioning System (GPS) can be accessed. The two single drum rollers driven one after the other can also, however, be coupled together via radar, ultrasound, infrared, etc. Of course, a rigid coupling using a rod is also possible.
It has also proven to be advantageous that the two compaction checking devices can be calibrated in order to then be able to offset differences in recording the measurement values. In particular, it is proposed for the calibration to set the two vibration roller drums on elements with known and/or equal dynamic rigidities, for example, blocks made of elastic material, and then to adjust the resulting measurement values.
For the values determined during the compaction process, the evaluation unit should advantageously contain an additional delay element, with which the measurement results of the first compaction checking device are to be stored intermediately so that they can be compared with the measurement values of the second compaction checking device at the identical measurement location.
It is clear that the retention time of the delay element is dependent on the driving speed and the separation distance of the two vibration rollers that are coupled together.